.
Headline corrected
"We have ruled out anyone hurling a grenade at the stall of the STF (Special Task Force) commandos," the officer said, adding the incident was now being investigated as an accident.
The STF was not supposed to have live explosives at the exhibition venue, the officer said, adding that "an officer was showing a hand grenade to spectators when it went off" at the Bandaranaike Memorial International Conference centre.
"We suspect the man was trying to show how to defuse a bomb when the blast occurred," a police investigator said.
"He had a hand grenade in one hand and an anti-personnel mine in the other.
"
Two STF commandos, two Buddhist monks and 13 exhibition-goers were wounded and taken to the Colombo National Hospital.
Thousands of people have visited the exhibition since Independence Day on Sunday and the military stalls were visited by large crowds.
Officials said there was no panic despite the blast.
"The STF stall closed imme